(1) Field of the Invention
The present invention relates to a data converter that realizes a data conversion system used for an authentication system and to a method thereof, in particular to a data converter that can be realized in an especially small size of implementation scale and has a high data confusion and to a method thereof.
(2) Description of the Related Art
In a challenge-response authentication system which is one of a method for examining a validity of a communication partner and the like, a secret conversion system is necessary for both authenticating and authenticated sides. As requirements for the secret conversion system, it is wished not only to have high data confusion performance (avalanche performance) but also to mount the method onto an apparatus at low cost.
As a conventional example of a data conversion system, there is a system of using a secret key encryption system. For example, in the case of where the challenge-response authentication system is realized by a data conversion system using a 56 bits key length Data Encryption Standard (DES) encryption system (for details about the DES encryption system, refer to Menezes, Alfred J., et al., “HANDBOOK of APPLIED CRYPTOGRAPHY”, CRC Press, 1997: 252-256), both of the authenticating side and the authenticated side secretly store a 56 bits key of the DES encryption system as an authentication key. Also, a plaintext and encrypted text of the DES encryption system are respectively determined as an input and an output for the data converting system. Accordingly, the DES encryption method can be used for a secret data converting system for an authentication (for details about the authentication system, refer to Menezes, Alfred J., et al., “HANDBOOK of APPLIED CRYPTOGRAPHY”, CRC Press, 1997: 400-403).
However, the secret key encryption system such as the DES encryption system is not constructed considering for sharing a circuit with other circuits that are mounted together with an encryption circuit in an apparatus. Therefore, it needs to be mounted as a circuit independent from other circuits. Accordingly, in a data conversion system using the conventional secret key encryption system, an encryption circuit is independently mounted separately from other circuits in the apparatus so that a scale of the circuit in the apparatus as a whole becomes large. That is, in order to realize an apparatus at a low cost, it is generally required to make a total scale of the circuit mounted in the apparatus smaller as possible. Therefore, it is desirable for the encryption circuit mounted in the apparatus to share the circuit with other circuits. However, it is not realized in the conventional structure.
Considering the above mentioned problem, the present invention aims to provide a data converter capable of reducing the total size of the implementation scale in an apparatus.